A. The more the better, but you should never allow your practice to a make mess of not only your normal life but also your Zen meditation by practising too hard. In the beginning, in order to get used to keeping the question, you had better make it a rule to practice for at least an hour a day at a set time everyday, for example, before going to bed or immediately after waking up. However, once you have learned how to keep the question, you need not confine your practice to a given period of time and be bound by time since time is a typical illusion which we should remove.
Then, erase all time lines from your mind and think that you practice all the time forever. Identify yourself with the question. Then whatever you do, your question will do it. Your question, for example, will drink tea when you drink tea, and your question will chat even when you chat. Then, your practice will go on by itself. Until you reach this stage, practice at least an hour a day and try to keep the question all the time.
All writing ©Boo Ahm. All images ©Simon Hathaway